Field of the Invention
The invention relates to an image-sensor structure, and more particularly to an image-sensor structure with a large exposed area of a back-side metal layer.
Description of the Related Art
An image sensor is a kind of semiconductor device that transforms optical images into electrical signals. Image sensors can be generally classified into charge coupled devices (CCDs) and complementary metal oxide semiconductor (CMOS) image sensors. Among these image sensors, a CMOS image sensor comprises a photodiode for detecting incident light and transforming it into electrical signals, and logic circuits for transmitting and processing the electrical signals.
During certain semiconductor manufacturing processes, such as an etching step (i.e. microlens protection (MP) etching step) for opening bond pads and scribe lines, electrostatic charges are generated and can accumulate on marginal back-side metal (BME). Unfortunately, when these electrostatic charges are discharged, they may pass through the substrate underneath, resulting in damage to the substrate due to the electrostatic discharge (ESD).
Therefore, development of a novel image-sensor structure which can effectively solve the problem of electrostatic discharge (ESD) during the microlens protection (MP) etching step for opening bond pads and scribe lines is desirable.